Antibacklash gearing



s. w. LARSON 2,440,901 Am I-BAcmsa GEARING Filed Jan. 31, 1947' 2 Sheets-Shut 1 INVENTOR .S/EGFR/EO M14050 Mw/M 2 uromvsrs May 4, 1948. 5 w LARSON 2,440,901

ANTI -BACKLASH GEARING Filed Jan. 31, 1947 2 Sheets-Sheet 2 BVLUM Q M grrmlvsrs 2,44%,991 ANTEACKJLASE GEAEING Siegfried W. Larson r litarby, 3a., assignor omoany, Philadelphia,

mania ii t invention relates to means for out the backlash in a train oi gears and has for an object the provision of anti -bacizlash means of on improved character and one in which friction is reduced to a minimum.

anti-backlash spring means of some kind is generally included in the train of gears to bias corresponding sides of the driving teeth against corresponding sides of the driven teeth of the gears. Generally the arrangement includes a pair of gears arranged side by side, the biasing force being-oppositely applied to the adjacent gears. In consequence, where they have been rotatably mounted on a statlonary shaft, they have operated under high frictlonal load and thus have required greater power for the transmission of a given amount of torque than is necessary in accordance with the present invention.

In carrying out the present invention in one form thereof, the intermediate gears to which the More supporting the intermediate gears is mounted in anti friction bearings. At least one of the intermediate gears is secured to the shaft While the other one is rotatably mounted thereon. In this manner, the application of the frictional force to the bearings is substantially en= tirely eliminated. it can only be effective when there is relative rotation between the adjacent gears and the deslgnis such that this relative motion rarely occurs during normal operation,

For a more detailed description or the invention, reference be had to the accompanying drawings, in which:

Fig. l is a fractional sectional view of the essential parts of the instrument to which the invention has been applied; and

Fig. 2 is a fractional view taken on the line 2-2 of Fit.

Referring to the drawings, the invention in one form has been shown as applied to a recording and indicating apparatus or" the type shown in U. S. Letters Patent No. 2,113,436 to Williams, Jr. Briefly, the recording and indicating apparatus consists of an index is movable across a scale it simultaneously with movement or" a stylus or pen it across a strip chart carried by a drum along a supporting rod i5 by means of a violin string or other suitable driving connection (not shown) from a shaft it. The shaft I 6 is driven devices of the prior art,

Q1 by motor 3'] which may be controlled by a mess urine netwo. such as shown in Williams, Jr, U. 55. Letters Patent No. 2,367,7l6, The motor ill, as will be evident from the aforesaid Williams patent, receives a major part of its energization from supply lines and theminor, direction-determining, part from an amplifier. Since power obtained from an amplifier is ordinarily of a low order, it is highly desirable to minimize to as great degree as possible the friction involved in the apparatus driven by the motor. Stated differently, it is relatively expensive to increase the power obtained from amplifiers and the less power that need be obtained to do a given job, the better is the design from the standpoint of initial and operating costs. Another desirable feature of design is to eliminate backlash in the gearing due solely to play or Heretofore, anti-backlash arrangements, though eliminating the backlash, have produced high bearing loads resulting in substantial friction in the gearing between the motor and the slidewire shaft.

In accordance with the present invention, the friction introduced by the antibacklash arrangement is greatly reduced over that present in the prior art devices and it is reduced to an amount which is small compared to that normally present in the gearing between the motor drive shaft and the slidewire shaft. More particularly, the motor ill has mounted on its drive shaft it an elon= gated pinion it. Two gears Eli and 2i mesh with The gear 29 is extension of a pinion gear 25, which is of course free to rotate with respect to the shaft 22. The gear 251 has its hub portion mounted over the hub portion of a pinion 2S and the two are secured to, and rotate with, the shaft 22 by means of a pin 2?.

Meshing with the pinion gears 25 and 26 are two gears '28 and lit. The gear 28 is secured to gear 29 is rotatably mounted on the hub 30 of the gear 28, the hub 36 extending upwardly along one side of gear 29 to hold it in position adjacent gear 28 and to present displacement along the shaft "5. The shaft l6 supports a variable-impedance device, such as a slidewire 3|, and it is also provided with a pulley 32 which, by suitable connection, such as a violin string, not shown, serves to move the pen carriage l4 laterally across the strip chart carried by the drum I3. I

Asshown in Fig. 2,-the gears 28 and 29 are interconnected by spring-biasing means comprising three tension springs 34, 35 and 36. In assembling the gear train, the gears 28 and 23 are rotated with respect to each other to place the springs 34-36 under tension adequate in magnitude to drive the shaft l6 without relative rotation between gears 26 and 29. After assembly and with the motor I'I at standstill, the springs 34-36 are effective on all of the gears between the driving gear l3 and the driven shaft It. More specifically, the springs bias the meshing teeth of gear 2| into engagement with one side of the teeth of the gear IS. The springs act oppositely on the gear 29 and, therefore, bias the teeth of the gear 26 against the other side of the teeth of gear l3. Thus, as the motor rotates in one direction, there is a direct drive from the elongated pinion I! through the gear 2|, and gears 26 and 28 to the shaft i6. When the motor I! rotates in the opposite direction, there is a drive from the teeth of gear is to the teeth of gear 20 and through gears 25, 29 and the springs 34-36 to the gear 23 and the shaft l6. Since the springs 34-36 have high initial tension, they transmit without further elongation a torque and thus provide the equivalent of a direct drive without backlash for rotation of the drive shaft l6.

Since the initial tension of the springs 34-36 is substantial, the forces applied thereby to the gearing affect the friction developed between the movable parts. With reference to the shaft 22, the gears 26 and 29 apply in opposite directions the force of the springs 34-36 to the shaft 22. If the pinion gears 25 and 26 were both free to rotate on the shaft 22, which would then be held stationary, the opposing forces would create substantial bearing pressures as between the pinions 25 and 26 and the stationary shaft. The high bearing pressure would result in a high frictional load because of the rotation of these gears relative to the stationary shaft. The friction would be present for all movements of the drive shaft l8. However, by mounting the shaft 22 in the bearings or journals 23 and 24 and securing the pinion 26 thereto with the pinion 25 rotatably mounted on the shaft 22, the aforesaid frictional load is to large degree eliminated. During rotation of the drive shaft It in either direction, there is no relativemovement between pinions 26 and 26 and the shaft 22. Relative movement may occur in event of irregularities in the gear teeth or during transmission of loads beyond the transmission capability gation. The provision of the bearings or journals 23 and 24 at the ends of the shaft and their positions remote from the pinions 25 and 26 which are mounted adjacent to each other, has the further advantageous effect of reducing the bearing load on the journals 23 and 24. Since these are anti-friction bearings, the anti-backlash device of the present invention introduces a negligible additional load on the motor I1.

It ma be further observed that the gearing illustrated results in substantial reduction in speed of the driven shaft l6 as compared with that of the motor. Obviously, any desired speed reduction or multiplication may be provided by of the springs without elonone of said terminal shafts suitably changing the diameters of the gears. If greater speed reduction be desired, additional sets of gears may be included which would be provided in pairs with hub assemblies corresponding with the gears 2e and 2! and their associated pinions 26 and 23, though they might be of materially diifering diameters. If it is desired to locate the motor at a greater distance from the driven shaft 16 than is shown inFig. 1, idler gears of desired diameter may be included, the hub assemblies again being the same as for the gears 20 and 2!.

While a typical application has been described, it is to be other modifications may be made within the scope of the appended claims.

What is claimed is:

l. A train of gears having two terminal shafts,

having secured thereto a first gear, a second gear rotatably supported on said shaft, spring-biasing means interconnecting said gears and biasing said second gear for rotation with respect to said first gear to take up the backlash of said train of gears, the other of said terminal shafts having an elongated single gear secured thereto, gears intermediat the gears on said terminal shafts, a shaft having secured thereto one of said intermediate gears, and rotatably supporting adjacent thereto another of said intermediate gears, and bearings rotatably supporting said last mentioned shaft in spaced relation from the gears carried thereby.

2. A train of gears having two terminal shafts, one of said terminal shafts having secured thereto a first gear, a second gear rotatably supported on said shaft adjacent said first gear, springbiasing means interconnecting said gears and biasing said second gear for rotation with respect to said first gear to take up the backlash of the train of gears, the other of said terminal shafts having an elongated single gear secured thereto, speed-changing gears characterized by the substantial reduction of bearing loads imposed by the bias transmitted from said first and second gears comprising gears intermediate, but meshing with, the gears on said terminal shafts, a shaft having secured thereto one of said intermediate gears, and adjacent .thereto rotatably supporting another of said intermediate gears, and bearings rotatably supporting said last mentioned shaft in spaced relation from the gears carried thereby.

3. A train of gears having two terminal shafts, one of said terminal shafts having secured thereto a first gear, a second gear rotatably supported on said shaft, spring-biasing means interconnecting said gears and biasing said second gear for rotation with respect to said first gear to take up the backlash of said train of of said terminal shafts having an elongated single gear secured thereto, gears intermediate the gears on said terminal shafts and meshing therewith, a shaft supporting intermediate the ends thereof said intermediate gears, bearings for said shaft located adjacent the end portions thereof and at substantial distances from the locations of said intermediate gears, and means for securing one of said intermediate gears for rotation with said last mentioned shaft, another of said intermediate gears being rotatably supported thereon.

4. A train of gears having two terminal shafts, one of said terminal shafts having secure thereto a first gear, a second gear rotatably supported on said shaft, spring-biasing means interconnecting said gears and biasing said second gear of the invention understood that gears, the other 6 for rotation with respect to said first gear to take shaft for rotatably supporting it, gears interup the backlash or said train of gears, one of said mediate the gears on said terminal shafts supterminal shafts having a single gear secured ported on said intermediate shaft, at least one substantial reduction of bearing loads imposed 5 intermediate gears being disposed in meshing by the bias transmitted from said first and second relation with the gears carried by said terminal gears comprising an intermediate shaft, bearings shafts.

disposed adjacent the ends of said intermediate SIEGFRIED W. LARSON.

Certificate of Correction Patent N 0. 2,440,901. May 4, 1948.

SIEGFRIED W. LARSON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 3, line 59, after the word occur insert only; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of September, A. D. 1948.

THOMAS F. MURPHY,

Aesistant Commissioner of Patents.

Certificate of Correction Patent No. 2,440,901. May 4, 1948.

SIEGFRIED W. LARSON It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 3, line 59, after the Word occur insert only; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 7th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

